New Drug Is Said to Offer Hope For Vaginal Gel to Block H.I.V.

Published: October 15, 2004

Scientists say they have a promising new lead in the quest to develop a vaginal gel that women could apply before sexual intercourse to block the AIDS virus.

The experimental drug, specifically designed to prevent the virus, H.I.V., from entering vaginal cells, is not ready for human testing. But it provided potent protection to female monkeys exposed to large amounts of a simian version of the AIDS virus, the researchers are reporting in the Friday issue of the journal Science.

The findings provide the first evidence that blocking the virus's preferred entry point is sufficient to prevent infection. Having such a target, said the lead researcher, Dr. Michael Lederman of Case Western Reserve University, ''could simplify approaches to prevention.''

AIDS specialists called the discovery a promising step in the quest for gels or creams that women could use to protect themselves without having to persuade their partners to use a condom. Topical microbicides, which would kill the virus on contact, have yet to realize their initial promise.

''There's been a lot of difficulty in getting microbicides to be both effective and nonirritating,'' Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, said. ''This is a step forward.''

The research was financed by the United States and Swiss governments. H.I.V. infection is rising more rapidly among women than men in many parts of the world. Half of all of infected adults are women, up from 41 percent in 1997, according to the Joint United Nations Program on H.I.V./AIDS. In sub-Saharan Africa, the group says, the figure is nearly 60 percent.

The first microbicide product promoted for protection against the AIDS virus, a spermicide called nonoxynol-9, was ultimately found to increase the chance of infection because it irritated vaginal tissue.

Now, two experimental microbicides are in the final stage of testing in thousands of women in Africa. While advocates hope they will provide at least partial protection, they are not directed specifically at the way the virus invades cells in heterosexual intercourse.

The invasion takes place at receptor molecules on cell surfaces, particularly a molecule called CCR5. Scientists have long known that people who lack CCR5 because of genetic mutations hardly ever get the virus and that the body harbors another molecule, Rantes, that can block the virus by sticking to CCR5.

Dr. Lederman teamed with Swiss researchers to create a version of Rantes thousands of times as potent as the natural molecule. They gave 30 monkeys a hormone to make them more vulnerable to H.I.V. infection, then sprayed their vaginas with the new chemical, called PSC-Rantes. Fifteen minutes later, the monkeys got high doses of the AIDS virus.

Monkeys who received the highest dose of the chemical were completely protected from the virus; a lower dose provided 80 percent protection. No side effects were detected.